The present invention relates to an improved oxygen scavenging system for use with oxygen sensitive materials, e.g., food, which system finds particular utility in the multi-layer films that includes an oxygen scavenging layer.
Oxygen scavenging materials have been developed partly in response to the food industry's needs of having longer shelf-life and better flavor preservation for packaged food.
These oxygen scavenging materials constitute at least a portion of the food package, and these materials remove oxygen which surrounds the food product, e.g., the residue oxygen in a package after sealing or air which has leaked into the package, thereby inhibiting spoilage of the food.
One method which is currently being employed involves the use of "active packaging" where the food product package is modified in some way to control the exposure of the food product to oxygen. Such "active packaging" can include sachets containing compositions, e.g., iron-based compositions such as Ageless.RTM. which scavenges oxygen in the package through an oxidation reaction. However, sachets are not advantageous for a variety of reasons not the least of which is the problems caused by the accidental ingestion of the sachets or the material present therein.
Recent attempts have involved incorporating an oxygen scavenger into the package structure itself. In such an arrangement, oxygen scavenging materials constitute at least a portion of the food package. One example of such an arrangement comprises a scavenging wall which includes inorganic powders and/or salts. See, for example, European Applications 367,835; 366,245; 367,390; and 370,802. However, such composition is difficult, if not impossible, to adequately process and thereby is not considered commercially feasible.
In another more promising arrangement, oxygen scavenging materials can be low molecular-weight oligomers that are typically incorporated into processable packaging polymers or can be oxygen scavenging polymers in which either the backbone is designed to break apart when the polymer reacts with oxygen or in which, initially at least, pendant oxidizable side chains react with oxygen.
Other methods which have been disclosed include that of European Patent Application 0454437, wherein an oxygen absorbent composition is disclosed. The composition contains a linear hydrocarbon polymer having one or more unsaturated groups or a mixture of linear hydrocarbon polymers having one or more unsaturated groups with an unsaturated fatty acid compound and an oxidation promoter as essential components. And, optionally, the composition can contain a basic substance and/or an adsorption substance.
European Patent Application 0424855 discloses an inhibitor parcel comprising a composition containing an unsaturated fatty acid compound as its main ingredient and a permeable diffusing parceling material prepared by laminating and bonding an oxygen permeable resin layer onto one side of a base sheet made of a fibrous material and an adhesive, and then laminating and bonding thereunto an oxygen permeable resin layer, and then laminating and bonding a porous film of a low softening point resin or a low softening point unwoven fabric onto the other side of the base sheet. The parcel is directed to preserving electronic devices and electronic parts and excluding oxygen as well as water.
Systems have also been designed to control odors which can be generated by deterioration of the contents (food) being stored, or deterioration of the film packaging used in storing the contents. For example, in Japanese Kokai Patent No. HEI6-223925, published Feb. 1, 1994, a deodorant packaging film is described. The packaging film is obtained by constructing a film having inner and outer surface layers of polypropylene resin that contains a polybutene or polyisobutylene, tackifier, and deodorant and constructing the middle layer from polyethylene terephthalate or a polyamide resin. The deodorant component of the polypropylene resin composition is described as being flavonoid deodorants, polyphenol components containing deodorants, deodorants that have turpentine oil as a major component, and deodorants based on organic acids.
U.S. Pat. No. 5,340,884 discloses a polyester/polyamide blend having an excellent gas barrier property and an improved flavor retaining property. In particular, the polyethylene terephthalate/low molecular weight polyamide blend reduces the concentration of acid aldehyde contained in the polyester, thereby rendering the blend more suitable for the storage of food.
U.S. Pat. No. 5,284,892 describes a system which is an aldehyde scavenging composition. Such compositions are useful in producing packaging films for oil containing foods, which give off aldehydes. The compositions comprises a polyalkylene imine and a polyolefin polymer. See also U.S. Pat. No. 5,362,784.
International Publication No. WO 93/01049 discloses a packaging composition that helps to extend shelf life of oil containing foods by absorbing undesirable aldehydes that are produced during oil degradation. The composition suggested to be used in absorbing the aldehydes are primary and/or secondary amine groups and strong inorganic bases.
European Patent Application 0504726 discloses a food preserving agent which comprises an oxygen absorbent and a substance which is able to remove acetaldehyde.
European Patent Application 0464782 is directed to a multi-layer thermoplastic film having a vinylidine chloride polymer barrier and at least a polyolefin second layer laminated to the barrier. Upon irradiation of the barrier layer, odor is generated due to ionizing irradiation of the barrier layer. Hydrotalcite is blended with the polyolefin in order to substantially reduce the odor generated by the vinylidine chloride copolymer barrier.
Japanese Kokai HEI5-247276 discloses an oxygen barrier resin composition. The oxygen barrier resin composition comprises a polyolefin, an oxidation catalyst and an odor absorbent. The odor absorbent is used to suppress the odor caused by oxidation of the polyolefin. As suitable absorbents, there are mentioned natural zeolite, synthetic zeolite, silica gel, activated carbon, activated clay, activated aluminum oxide, magnesium silicate, aluminum silicate and the like. Synthetic hydrotalcite type compounds can also be used.
A major problem that still needs to be addressed, however, is that a wide variety of organic compounds are produced upon oxidation of the oxygen scavenging material. Many of these oxidation products can migrate from the layer carrying an oxygen scavenging material and enter the air surrounding the food or even enter the food itself.
Such oxidation products can have foul odors or can even be compounds that are undesirable. It is therefore highly desirable to provide a way to prevent such oxidation products from entering a packaged volume that contains food.
One attempt to solve the problem of migration of oxidation products involves the use of a composition comprising two layers, where one layer carries an oxygen scavenging material and one layer is a barrier situated between the packaged volume and the layer carrying an oxygen scavenging material. See U.S. application Ser. No. 08/304,303, filed Sep. 12, 1994, now abandoned, which is incorporated herein by reference for all purposes.
One problem with this approach is that many barriers are capable of blocking the migration of molecules of certain sizes, but they fail in blocking very small organic molecules. On the other hand, there are good barriers which are effective to block the migration of small oxidation products into, e.g., the enclosed volume of the package, but they also slow the oxygen migrating from the enclosed volume to the organic scavenging material.
Other multi-layer film packaging materials are also recognized within the art. Such films can include, in addition to the layers discussed above, a "polymeric selective barrier layer" such as that described in U.S. application Ser. No. 08/304,303, filed Sep. 12, 1994 now abandoned. While such selective barrier layers can prevent the migration of certain, in fact many, of the undesirable oxidation products, certain by-products, and in particular, those having a smaller molecular size may not be effectively blocked. This is particularly true for those by-products which are of a similar or slightly larger size to gaseous oxygen.
Thus, the need still exists for an improved system for protecting oxygen sensitive materials, and in particular a system applicable to multi-layer film for use in food packaging which is capable of neutralizing such molecules, thereby reducing those problems associated with these by-products as discussed above.